The novel coenzyme independent L-sorbose dehydrogenase is an enzyme which catalyzes the oxidation of L-sorbose to L-sorbosone, the precursor of 2-keto-L-gulonic acid which is an important intermediate for the production of vitamin C.
A reaction to convert L-sorbose to L-sorbosone has been known in microorganisms. L-sorbosone production from L-sorbose using cell free extracts of microorganisms was reported in several prior publications. In U.S. Pat. No. 3,912,592, the microorganisms belonging to the genus Gluconobacter, Pseudomonas, Acinetobacter, Bacillus, Sarcina, Streptomyces, Serratia, Aerobacter, Mycobacterium and Paecilomyces were reported to be capable of such a conversion. Although Makover et al. (Biotechnol. Bioeng. 17, 1485-1514, 1975) described the primary characterization of the enzyme of Pseudomonas putida ATCC 21812, they have failed to isolate it. Kitamura et al. (Biotechnol. Bioeng. 17, 349-359, 1975) reported that the activity of L-sorbose dehydrogenase found in Gluconobacter melanogenus IFO 3293 was stimulated by phenazine methosulfate, methylene blue or potassium ferricyanide as an electron acceptor. But they did not isolate the enzyme.
As described above, no purified enzyme has been obtained or prepared which has the activity of catalizing the oxidation of L-sorbose to L-sorbosone.